Despite his recent victories, securing the Republican presidential nomination will take more work – perhaps beyond Super Tuesday.

Reporting from Atlanta — As the Republican contenders turn in earnest to the Super Tuesday states, Mitt Romney's next challenge is to convert a slender Michigan win into something bigger: an unshakable lead in the presidential contest.

Rick Santorum's runner-up primary finishes Tuesday there and in Arizona left the party establishment breathing easier, though there seemed little optimism that the nomination fight, which has sapped the resources of donors and weakened the likely GOP nominee's standing with independent voters, would end anytime soon.

"Romney is a fragile front-runner, but there is much less panic in Republican ranks than there was 24 hours ago," said Washington lobbyist Ed Rogers, a White House political advisor in the Ronald Reagan and George H.W. Bush administrations. "The notion of Santorum at the top of the ticket frightened a lot of people. That chance has been reduced, but it hasn't been extinguished."

Rogers, a donor to several GOP presidential candidates, including Romney, said that if the former Massachusetts governor does extremely well in the March 6 tests, "you'll start to hear people of stature call for an end to this." But even Romney advisors regard that as unlikely. Instead, it could take months before any contender can put a mathematical lock on the 1,144 delegates needed to win the nomination.

Tucker Eskew, a nonaligned Republican strategist, said the "lack of enthusiasm" for Romney "was not really altered by the results" of Tuesday's primaries. Among Republican voters, though, "there's an openness to getting there. What Gov. Romney has got to do is build on it."

This year, Republicans are looking for "a full-spectrum communicator," he added. "We may not get that." What Romney needs to do is "maintain some authority over the narrative" of the campaign, which "the press, his opponents and Democratic forces are constantly trying to degrade," said Eskew, an advisor in George W. Bush's White House and a campaign aide for John McCain in 2008.

Romney, he said, had repeatedly faltered, through "a series of unforced errors, a paucity of convincing wins and his much-discussed difficulty in focusing and staying focused on the economy."

On Wednesday, at least, Romney locked in on economic issues — promising a small crowd at a rainy rally in Toledo, Ohio, that he would crack down much harder on China for unfair trade practices than President Obama has. He avoided mention of his GOP rivals.

Santorum, meantime, was in Tennessee, another March 6 primary state. Behind the scenes, his campaign was pushing for resolution of the delegate count in Michigan. The final tally is expected to show a near-even split with Romney — the state allocates delegates largely by congressional district — and Santorum tried to claim a belated moral victory despite his 3-point loss in the overall vote.

Michigan "was a huge win for us," Santorum told reporters, after speaking to a crowd of about 1,000 at Temple Baptist Church in Powell, Tenn., near Knoxville, many of them conservatively dressed students from nearby Crown College. "We are out here today heading to Super Tuesday with some wind at our back."

His aides, meantime, were striving to prevent a repeat of their Iowa experience, when an announcement of Santorum's caucus win was delayed for weeks by party officials.

Next Tuesday, Republican voters will award the biggest delegate haul so far this year — more than 400 in all. What's been dubbed Super Tuesday, however, is considerably less super than past versions, as fewer states hold contests on that day and new party rules spread the delegates more proportionally among the GOP contenders. As a result, the eight primaries and three caucuses are unlikely to generate a decisive overall victory for anyone.

Romney is favored in three Eastern primaries: Vermont, Virginia and the state he served as governor, Massachusetts. Santorum is expected to have the advantage in Tennessee and Oklahoma, which have socially conservative electorates.

Ohio, a general election battleground and the main Super Tuesday event, will be a Rust Belt rematch in an environment less friendly to Romney than his native Michigan. The primary electorate is more conservative, with a larger religious-conservative component and a significant tea-party faction, all of which favor Santorum. And, in a twist, it's the former senator who may be playing on home turf.

"We feel our message, which is about a guy from a steel town in western Pennsylvania, is going to play very, very well across the state of Ohio," said Santorum, who once represented a Pittsburgh-area district in Congress.